The present invention relates broadly to an electrically-heated hose assembly, and more particularly to such an assembly for use in transferring a urea, i.e., carbamide, solution in a diesel engine emissions after-treatment system.
Selective catalytic reduction (SCR) is a method of converting nitrogen oxides (NOx) into diatomic nitrogen (N2O) and water with the aid of an emission reduction reagent such as urea. SCR is used to reduce emissions in diesel engines such as for ships, locomotives, gas turbines, and trucks.
SCR systems inject a liquid urea solution or other catalyst into a stream or flue of exhaust gas. The exhaust gas is absorbed into the urea solution whereupon the nitrogen oxides (NOx) in the gas are converted into diatomic nitrogen by means of a chemical reaction
The basic components of a urea-based SCR system, such as may be used on a heavy duty truck for example, are a urea solution tank, pressure regulators, a control unit, temperature sensors, a dosing module, and a pump. To link these components for the purpose of transferring urea through the system, flexible hose assemblies are employed. Many of these assemblies use plastic-bodied quick-connect fittings, such as specified in Society of Automotive Engineers (SAE) Standard J2044, to allow for the assembly and disassembly of the system components.
A common problem of urea-based SCR systems is the relatively high freezing point of the urea solution. The freezing temperature of urea is about +13° F. (−10.6° C.). When freezing occurs, the SCR system is rendered non-operational because the urea catalyst solidifies and cannot be pumped through the hose assemblies into the exhaust stream. Since it is not unusual to encounter temperatures of +13° F. (−10.6° C.) and below in many northern climes, urea-based SCR systems typically are designed with heated hoses and other types of heaters to maintain the temperature of the urea solution above +13 F. SCR systems and components are further described, for example, in U.S. Pat. Nos. 7,578,321; 5,976,475; and in EP 1,937,946; and WO 2007/032033. Heated hoses of general types are shown, for example, in U.S. Pat. Nos. 6,738,566; 6,727,481; 5,910,266; 5,791,377; 5,511,530; 5,428,706; 4,815,769; 4,553,023; 4,455,474; 4,372,279; 4,038,519; 3,355,572; and 3,522,413.
As applications for urea-based SCR systems continue to increase, it is believed that improvements in electrically-heated hose constructions would be well-received. Especially desired would be a construction which is flexible and light-weight, and which is economical to manufacture.